1. Field of the Invention
The invention relates to a processing method, and more particularly to a color interpolation processing method.
2. Description of the Related Art
FIG. 1a shows a structure for an image sensor module. Scene is captured by lens 11. A color filter array (CFA) 12 comprises color filters R, B, and G for acquiring color components. A charged-coupled device (CCD) 13 or an active pixel sensor (APS) comprises a plurality of pixel units. Each pixel unit transforms color components into electronic signals and stores the electronic signals.
One color component is acquired by one color filter. Thus, only one color component is available in each pixel unit such that the other two of the three color components are missing from each pixel unit. To completely display the scene 10, various color interpolation methods are utilized. The color interpolation methods determine the other two missing color components according to the filtered and stored color component.
One color interpolation method by S. C.Pei et al in IEEE Trans. Circuits and Systems for Video Technology, VOL. 13, NO. 6, June 2003 describes “Effective Color Interpolation in CCD Color Filter Arrays Using Signal Correlation”.
FIG. 1b is a schematic diagram of the CFA. The color interpolation method disclosed by S. C. Pei et al obtains a missing G7 value according to a known R7 value. The missing G7 value can be recovered as (1).
                              G          ⁢                                          ⁢          7                =                              R            ⁢                                                  ⁢            7                    +                                    1              4                        ⁢                          (                                                                    K                    R                                    ⁢                  3                                +                                                      K                    R                                    ⁢                  6                                +                                                      K                    R                                    ⁢                  8                                +                                                      K                    R                                    ⁢                  11                                            )                                                          (        1        )            
wherein, KR3 is defined as in (2), KR6 is defined as in (3), KR8 is defined as in (4), and KR11 is defined as in (5).
                                          K            R                    ⁢          3                =                                            G              ⁢                                                          ⁢              3                        -                          R              ⁢                                                          ⁢              3                                =                                    G              ⁢                                                          ⁢              3                        -                                          1                2                            ⁢                              (                                                      R                    ⁢                                                                                  ⁢                    1                                    +                                      R                    ⁢                                                                                  ⁢                    7                                                  )                                                                        (        2        )                                                      K            R                    ⁢          6                =                                            G              ⁢                                                          ⁢              6                        -                          R              ⁢                                                          ⁢              6                                =                                    G              ⁢                                                          ⁢              6                        -                                          1                2                            ⁢                              (                                                      R                    ⁢                                                                                  ⁢                    5                                    +                                      R                    ⁢                                                                                  ⁢                    7                                                  )                                                                        (        3        )                                                      K            R                    ⁢          8                =                                            G              ⁢                                                          ⁢              8                        -                          R              ⁢                                                          ⁢              8                                =                                    G              ⁢                                                          ⁢              8                        -                                          1                2                            ⁢                              (                                                      R                    ⁢                                                                                  ⁢                    7                                    +                                      R                    ⁢                                                                                  ⁢                    9                                                  )                                                                        (        4        )                                                      K            R                    ⁢          11                =                                            G              ⁢                                                          ⁢              11                        -                          R              ⁢                                                          ⁢              11                                =                                    G              ⁢                                                          ⁢              11                        -                                          1                2                            ⁢                              (                                                      R                    ⁢                                                                                  ⁢                    7                                    +                                      R                    ⁢                                                                                  ⁢                    13                                                  )                                                                        (        5        )            
A missing B7 value can be obtained according to the missing G7 value defined by (1). The missing B7 value is calculated as
                              B          ⁢                                          ⁢          7                =                              G            ⁢                                                  ⁢            7                    +                                    1              4                        ⁢                          (                                                                    K                    B                                    ⁢                  2                                +                                                      K                    B                                    ⁢                  4                                +                                                      K                    B                                    ⁢                  10                                +                                                      K                    B                                    ⁢                  12                                            )                                                          (        6        )            
wherein operations of KB2, KB4, KB10, and KB12 are similar to KR3, KR6, KR8, and KR11.
Although the missing value is obtained by the color interpolation method disclosed by S. C. Pei et al, the color interpolation method does not particularly take the edge pattern into account. Therefore, the method would induce the false colors and blur the pattern around the edges.
Another color interpolation method by X.Wang et al in ICICS-PCM 2003 describes “Edge-Adaptive Color Reconsruction for Single-Sensor Digital Camera”.
The color interpolation method disclosed by X. Wang et al detects an edge pattern in a G channel and calculates a G value at R or B pixel in the edge pattern. Next, the color interpolation method utilizes a weighted method to calculate an absolute difference value between a horizontal direction of the G channel and a vertical direction of the G channel for obtaining an R value at an unknown R pixel and a B value at an unknown B pixel.
The color interpolation method disclosed by X. Wang et al usually detects the incorrect edge pattern such that the incorrect value is generated. Additionally, since the weighted method is more complex, the cost of the hardware is increased.
Another color interpolation method by Y. M. Wu et al in Image Analysis and Interpretation, 2004. 6th IEEE Southwest Symposium describes “Color Interpolation for Single CCD Color Camera”. The color interpolation method utilizes a weighted method to calculate the unknown G, B, R values. The accuracy is higher, however, the cost of the hardware is higher.